Studies on a liquid crystal display have been developed as to the technique for controlling the luminance of light emitted from a backlight in accordance with a video signal, in order to improve the contrast of the video to be displayed and to reduce power consumption.
According to a general method, a screen is divided into a plurality of areas, and the luminance of a light source arranged in each area is separately controlled in accordance with a video signal.
When the luminance of the light sources is reduced as a result of the luminance control, the signal value is expanded to maintain the luminance to be displayed. As a method to reduce gradation saturation caused by this expansion, it is suggested to set an expansion gain smaller as the signal value becomes larger in order to prevent gradation saturation.
However, in the above conventional technique, expansion gains each differing depending on each pixel position must be calculated to calculate a nonlinearly expanded signal value of the input signal value using the expansion gains. Accordingly, there is a problem that computing amount is enormously increased.